<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Example</title>
  <style>
    body {
      height: 3000px;
    }
    .dot {
      width: 2px;
      height: 2px;
      background-color: black;
      position: absolute;
    }
  </style>
</head>
<body>
<script>
  (function() {
    "use strict";

    document.onmousemove = handleMouseMove;
    function handleMouseMove(event) {
      var dot, eventDoc, doc, body, pageX, pageY;

      event = event || window.event; // IE-ism

      // If pageX/Y aren't available and clientX/Y
      // are, calculate pageX/Y - logic taken from jQuery
			// Calculate pageX/Y if missing and clientX/Y available
      if (event.pageX == null && event.clientX != null) {
        eventDoc = (event.target && event.target.ownerDocument) || document;
        doc = eventDoc.documentElement;
        body = eventDoc.body;

        event.pageX = event.clientX +
          (doc && doc.scrollLeft || body && body.scrollLeft || 0) -
          (doc && doc.clientLeft || body && body.clientLeft || 0);
        event.pageY = event.clientY +
          (doc && doc.scrollTop  || body && body.scrollTop  || 0) -
          (doc && doc.clientTop  || body && body.clientTop  || 0 );
      }

      // Add a dot to follow the cursor
      dot = document.createElement('div');
      dot.className = "dot";
      dot.style.left = event.pageX + "px";
      dot.style.top = event.pageY + "px";
      document.body.appendChild(dot);
    }
  })();
</script>
</body>
</html>